Candida albicans, a diploid asexual yeast, is a major cause of systemic fungal infections, particularly in patients with acquired immunodeficiency syndrome (AIDS).
Species of the genus Candida are part of the normal human flora and are the most common yeast pathogens. Candida albicans, a dimorphic, asexual yeast, is the most frequently identified pathogen among Candida species. Systemic Candida infections commonly occur in patients who have been immunocompromised by treatment with immunosuppressive medication and broad spectrum antibiotics.
At the present time, therapy for a patient afflicted with systemic C. albicans infection is treatment with amphotericin B alone or in combination with the nucleoside analog 5-fluorocytosine. Alternatively, lanosterol 14.alpha.-demethylase inhibitors such as the imidazole ketoconazole or the triazole fluconazole are used. While amphotericin B is an effective fungicidal agent, it is nephrotoxic, does-not penetrate into the cerebrospinal fluid, and must be given intravenously. Ketoconazole and the newer azoles are fungistatic rather than fungicidal.
A series of n-alkoxyacetic acids has been tested for effects on the growth of a variety of fungal species, including C. albicans, in Sabouraud dextrose agar, with 3-oxaundecanoic acid showing the broadest spectrum and highest potency and several other compounds, including 3-oxatetradecanoic acid, inhibiting growth Gerson et al, J. Pharmaceut. Sci., 68, 82-84 (1979)!.
U.S. Pat. No. 5,073,571 describes ether containing fatty acid compounds such as 13-oxatetradecanoic acid which have been evaluated as antiviral agents, e.g. against retroviruses such as HIV-1. The compound 13-oxatetradecanoic acid, which is a substrate for human acyl CoA synthetase and human myristoylCoA:protein N-myristoyltransferase (NMT), inhibits HIV-1 replication in acutely and chronically infected human T-lymphocyte cell lines at doses which do not cause cellular toxicity B. Devadas et al, J. Biol. Chem., 267, 7224-7239 (1992)!. Studies with tritiated 13-oxatetradecanoic acid indicate that this fatty acid analog is incorporated into HIV-1 Pr55.sup.gag and nef and some, but not all, cellular proteins Bryant et al, Proc. Nat 'l. Acad. Sci. USA, 88, 2055-2059 (1991)!.
N-myristoylation of proteins is catalyzed by myristoylCoA:protein N-myristoyltransferase (NMT.sup.1, N-myristoyltransferase). NMT transfers myristate (C14:0) from myristoylCoA to the amino-terminal Gly residue of proteins in such diverse eukaryotic species as animals, plants, and fungi J. K. Lodge et al, J. Biol. Chem., 269, 2996-3000 (1994)!. This modification is required for the biological functions of a variety of cellular and viral proteins D. R. Johnson et al, Ann. Rev. Biochem., in press, (1994)!. The NMT1 gene is essential for vegetative growth of S. cerevisiae. Moreover, haploid strains of S. cerevisiae containing a nmt1 null allele are not viable R. J. Duronio et al, Proteins, Structure, Function, and Genetics, 13, 41-56 (1992c)!. Metabolic labeling studies indicate that S. cerevisiae produces at least 12 N-myristoylproteins during exponential growth R. J. Duronio et al, J. Cell. Biol., 113, 1313-1330 (1991)!. Two functionally interchangeable ADP ribosylation factors, Arf1p and Arf2p, have been identified as N-myristoylproteins T. Stearns et al, Mol. Cell. Biol., 10, 6690-6699 (1990)!. Metabolic labeling studies have shown that a laboratory strain of C.albicans (B311) synthesizes a small number of cellular N-myristoylproteins during exponential growth in rich media The C.albicans NMT gene has been isolated. Its 451 amino acid protein product shares 55% identity with the S. cerevisiae acyltransferase R. C. Wiegand et al, J. Biol. Chem., 267, 8591-8598 (1992)!. Two ARF genes have also been indentified in C. albicans C. A. Langner et al, J. Biol. Chem., 267, 17159-17169 (1992)!. At least one of them is a substrate for NMT J. K. Lodge et al, J. Biol. Chem., 269, 2996-3000 (1994)!. Although C. albicans does not have a known sexual pathway, nonetheless it synthesizes a protein, Cag1, which is homologous to S. cervisiae Gpalp C. Sadhu et al, Mol. Cell. Biol., 12, 1977-1985 (1992)!. The amino terminal sequence of Cag1 (GCGASVPVDD) makes it a likely substrate for S. cerevisiae Nmt1p D. A. Towler et al, Ann. Rev. Biochem., 57, 69-99 (1988b)!. Moreover, CAG1 can complement the growth arrest and mating defects found in strains of S. cerevisiae with gpa1 null alleles C. Sadhu et al, Mol. Cell. Biol., 12, 1977-1985 (1992)!.
The peptide substrate specificities of C. albicans and S. cerevisiae NMTs are considerably different than that of human NMT W. J. Rocque et al, J. Biol. Chem., 268, 9964-9971 (1993)!. However, surveys of a large panel of myristic acid analogs indicate that the acylCoA binding sites of the orthologous enzymes are quite similar N. S. Kishore et al, J. Biol. Chem., 268, 4889-4902 (1993) footnote 2!. This apparent divergence in the peptide but not acylCoA binding sites undoubtedly reflects the similar requirements of these NMT enzymes for myristoylCoA and the marked differences in the numbers and types of protein substrates they must acylate in vivo D. A. Rudnick et al, Adv. Enzymol., 67, 375-430 (1993)!.
Interaction between Saccharomyces-cerevisiae-derived myristoyl-CoA:protein N-myristoyltransferase (Nmtlp) and. photoactivatable .sup.125,-labeled octapeptides has been studied in the presence of other high-affinity peptide substrates and competitive inhibitors of such labeled octapeptides, such other peptide substrates and competitive inhibitors being the peptides GLYASKLS-NH.sub.2 and ALYASKLS-NH.sub.2, respectively D. A. Rudnick et al, Proc. Natl. Acad. Sci., 90(3), 1087-1091 (1993)!